An internal combustion engine, such as for a motor vehicle, is generally required to have some form of exhaust aftertreatment device to combust and/or reduce pollutants created during the combustion process, prior to their escape into atmosphere. A typical exhaust aftertreatment device, also referred to as a catalytic converter, operates to store, reduce and/or oxidize pollutants as they pass through, prior to expelling them into the atmosphere. The typical catalytic converter comprises a coated ceramic or metallic substrate contained within a metallic structure, which is integrated into an exhaust system. A catalytic converter is generally larger in diameter than the exhaust system into which it is placed. Therefore, the catalytic converter typically includes flow transition devices, often referred to as end cones. One type of catalytic converter, referred to as an internally insulated catalytic converter, employs a pair of coaxial end cones on each end of the catalytic converter. An outer circumference of a face of an external end cone is welded to a face of the metallic structure of the catalytic converter, whereas a corresponding face of an internal end cone interfaces with insulating material in an annular space between the metallic structure and the substrate. A space is created between the inner end cone and the outer end cone which may be filled with insulating material or ambient air.
A typical substrate is wrapped in insulating material along its longitudinal circumference and inserted into the metallic structure. The insulating material structurally supports for the substrate, provides vibrational damping by decoupling the substrate from the metallic structure and the exhaust system, and provides a gaseous seal between the substrate and the metallic structure such that substantially all exhaust gases flow through passageways within the substrate.
A typical substrate includes a plurality of flow channels which pass longitudinally therethrough, for passing of exhaust gases therethrough. Substrates are characterized by the number of flow channels, or cells, they contain in a facial area of the substrate, e.g. cells per square inch, and by thickness of the substrate wall between each of the cells, e.g. 4 mil or 6.5 mill.
Under normal operation of an internal combustion engine, a small amount of the insulating material supporting the substrate may erode, or attrit over the service lifetime of the catalytic converter. The volume of eroded insulating material is insubstantial over the life of the converter, and typically passes through the substrate cells.
However, engine and vehicle manufacturers are requiring substrates with higher cell densities and thinner walls between cells, to help meet more stringent emissions regulations and to allow more efficient packaging of the converter. Substrates with higher cell densities and thinner walls are less able to pass the eroded insulating material, resulting in eroded insulating material building up on the leading face of the substrate. This may cause increased exhaust flow restriction, resulting in reduced engine power and other related engine and vehicle problems well known to one skilled in the art. The problem of exhaust flow restriction may be further exacerbated by deposition of oil, fuel and other residuals of the combustion process accumulating on the eroded insulating material. Therefore, what is needed is a device and method to prevent erosion of the insulating material during the service life of the converter, over ongoing operation of the engine. Such a device needs to be operable to withstand sustained exposure to extreme temperatures and flows occurring during useful life of the converter. It is also preferable that such a device and method meets the above-mentioned needs without requiring changes to existing designs, and tools and processes used to manufacture converters.